1. Technical Field
The present invention generally relates to evaporative emission control systems for automotive vehicles and, more particularly, to a leak detection assembly and a method of determining if a leak is present in an evaporative emission control system of an automotive vehicle.
2. Discussion
Modern gasoline powered automotive vehicles typically include a fuel tank and an evaporative emission control system that collects fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing activated carbon, to collect and store fuel vapors. The canister collects fuel vapors which are displaced from the fuel tank during refueling of the automotive vehicle or from increases in fuel temperature.
The evaporative emission control system also includes a purge valve between the intake manifold of the engine and the canister. When conditions are conducive to purging, a controller opens the purge valve a predetermined amount to purge the canister. That is, the collected fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within the engine.
It has recently become desirable to check evaporative emission control systems for leaks. To this end, on board vehicle diagnostic systems have been developed to determine if a leak is present in a portion of the evaporative emission control system. One such diagnostic method utilizes negative pressurization to check for leaks. In this method, a vent valve is used to seal the canister vent, a sensor to monitor system pressure, and a purge valve to draw a vacuum on the evaporative emission control system. As the vacuum is drawn, the method monitors whether a loss of vacuum occurs within a specified period of time. If so, a leak is presumed to be present.
Diagnostic systems also exist for determining the presence of a leak in an evaporative emission control system which utilize positive pressurization rather than negative pressurization. In positive pressurization systems, the evaporative emission control system is pressurized to a set pressure, typically through use of an air pump. Thereafter, a sensor detects whether a loss of pressure occurs over a certain amount of time.
While positive and negative pressurization systems are useful, there is room for improvement in the art. For instance, it would be desirable to provide a leak detection system which does not require either positive or negative pressurization of the system from an outside source. Additionally, it would be desirable to provide a leak detection system which functions when the vehicle is not operating. This would eliminate many of the complicated issues which make leak detection on an operating vehicle very difficult.